Food N'eeds of a Worling Horse 373 



than the coefficient of usefnl work fonnd b}' ^Yolff, 

 whose conclusions Znntz regards as erroneous. But 

 even if Zuntz's figures are none too low, it is evident 

 that the animal machine uses fuel with much greater 

 economy than a steam engine where the coefficient of 

 usefulness might not be over 10 per cent. The figures 

 he reached show further that the total expenditure of 

 energy by a horse weighing 1,000 pounds in walking 

 one mile equaled 453 foot tons, which would be fur- 

 nished by .164 lb. of digestible food. As 44.4 per 

 cent of this, or 201 foot tons, was due to the effort 

 of walking over and above the needs for maintenance, 

 the extra digestible food needed per mile of walking 

 was .07216 lb. 



Zuntz also found that when a horse increases the 

 external mechanical labor performed such increase costs 

 .001155 lb. digestible dry matter for each foot ton of 

 work. On this basis the 264 foot tons of energy 

 which is needed for pulling one mile a load with a 

 draft of 100 lbs. would be furnished by .3049 lb. of 

 food matter. The total food expenditure, therefore, 

 for walking and a draft of 100 lbs. over a smooth, 

 level road for one mile, would be .377 lb. digestible 

 nutrients, and for twenty miles 7.54 lbs. If we add 

 to this the 6.4 lbs. needed for mere maintenance, we 

 have 13.94 lbs. digestible matter as the proper ration for 

 a horse doing the work stated for a distance of 20 miles. 

 These figures are certainh' not inconsistent with the 

 standard reached by other methods for a horse doing 

 average work. Such a calculation is at least useful 

 in showing the direct relation of food expenditure to 



